Bleaching of wool



Patented Apr. 27, 1954 \in tiCH Mu BLEACHING OF WOOL John J. McGovern,Wilmington, Del., asslgnor to E. I. du Pont de Ncmours and Company,Wilmington, Del., a corporation of Delaware No Drawing. Application July7, 1950, Serial No. 172,611

3 Claims.

This invention relates to the bleaching of wool with alkaline peroxidesolutions and more particularly to a method whereby wool may be bleachedwith such solutions with minimum damage resulting.

Wool is commonly bleached with alkaline peroxide solutions. Solutions oflow peroxide concentrations are generally employed at relatively lowtemperatures and for relatively long times in order to avoid excessiveoxidative degradation of the wool. Wool is readily damaged by alkalineperoxide solutions and the extent of such damage is indicated by thealkali solubility of the wool. If badly damaged, the bleached wool willnot satisfactorily withstand even mild washing with soap and water.

It is an object of the invention to provide a method of bleaching woolwith alkaline peroxide solutions with minimum damage to the woolresulting. A further object is a method whereby wool may be bleachedrapidly and at relatively high temperatures with alkaline peroxidesolutions without excessive degradation of the wool. Still furtherobjects will be apparent from the following description.

It is known that formaldehyde will combine loosely with wool. It is alsowell known that formaldehyde reacts readily with alkaline peroxide. Thisreaction proceeds rapidly and quantitatively to destroy bothformaldehyde and hydrogen peroxide and to produce sodium formate,

water and hydrogen according to the following equation:

The Blank and Finkenbeimer (Ber. 31, 2979 (1898)) method of formaldehydeanalysis is based on this reaction. In view of the loose nature of thecombination of formaldehyde with wool and the ease and rapidity withwhich formaldehyde reacts with hydrogen peroxide, it would have beenexpected that alkaline peroxide solutions would remove formaldehyde fromits combination with wool and destroy it with resultant consumption ofperoxide, and that, therefore, no substantial beneficial action wouldresult from the treatment of wool with formaldehyde prior to bleachingwith alkaline peroxide solutions. On the contrary, it would have beenexpected that peroxide consumption would be excessive, which would bedisadvantageous.

Contrary to expectations it has been discovered that in the bleaching ofwool with alkaline aqueous hydrogen peroxide solutions, substantialadvantages result from the pretreatment of the W001 with formaldehyde,provided such pretreatment is carried out under such conditions that thecombined formaldehyde content is at least 0.3% and preferably 0.5 to 1%,based on the weight of the wool, and that when so pretreated, wool maybe rapidly bleached at elevated temperatures without excessive peroxideconsumption and with minimum damage to the wool resulting. In accordancewith the invention, the wool which is to be bleached is treated with anaqueous formaldehyde solution under such conditions as will effect acombined formaldehyde content of at least 0.3% and preferably from 0.5to 1%, after which the wool is bleached with an alkaline hydrogenperoxide solution.

In present wool bleaching methods using alkaline peroxide solutions,temperatures above about -130 F. are generally avoided in order to avoidexcessive degradation of the wool. At such temperatures 6 to 16 hoursare usually required to obtain a satisfactory bleach. It has beendiscovered that when wool has been pretreated so as to contain at least0.3% and preferably 0.5 to 1% of combined formaldehyde, it may bebleached successfully at substantially higher temperatures in muchshorter times without excessive degradation of the wool. Thus at F. goodbleaching can be effected in 1 hour or less with minimum of damage tothe wool.

The combined formaldehyde content should be at least 0.3% in order toprovide worth while protection against damage by the alkaline peroxide.In order to effect combination of that amount of formaldehyde, the woolshould be contacted with a formaldehyde solution having a pH of about 2to 10 and a concentration of at least about 0.1% CHzO. The preferred pHis about 4 to 9. The use of solutions of concentrations above about 5%offers no particular advantage and concentrations of about 0.3 to 2% arepreferred. The time of treatment will depend chiefly on theconcentrations and temperatures used, the higher the concentration ortemperature the shorter the time required to obtain the desired amountof formaldehyde combined with the wool. At concentrations within thepreferred range and at temperatures of 120-180 R, which are preferred,treating times of from about 2 to 30 minutes, and generally about 5 to15 minutes, are adequate and result in combined formaldehyde values offrom around 0.5 to 1.0%. Larger amounts of formaldehyde can be combinedwith the wool, but they offer no advantages over the preferred amounts.

The invention is illustrated by the following examples.

EXAMPLE 1 Skeins of Wool weighing 45 g. each were scoured by immersionfor 10 minutes in water at 120 F. containing 1 g. of soap and 1 g. of28% NHrOH per liter. The skeins were then washed thoroughly and dividedinto two groups. The skeins of the first group were bleached in peroxidebleach baths under the conditions indicated in Table 1. Comparativebleaching tests were run on the second group of skeins after they hadfirst been soaked for 30 minutes in 1 liter of Water containing 4.5 g.CH2O and having a pH of 6.5 and a temperature of 120 F., then rinsedthoroughly with water to remove uncombined formaldehyde. Thispretreatment with formaldehyde resulted in a combined formaldehydecontent of about 0.8%. All bleaching tests in both series were carriedout using 1 liter of bleach solution having a pH of 9.6 and containingg. sodium pyrophosphate as a stabilizer for the peroxide. Followingbleaching, the alkali solubilities and degree of whiteness of the woolsamples were determined.

the formaldehyde-pretreated sample was relatively high because thebleaching time was much longer than necessary. However, it will be notedthat the corresponding sample which had not been pretreated withformaldehyde had a solubility of 52%, or almost three times as high.

EXAIWPLE 2 Samples of scoured skeins of wool each weighing 45 g. weretreated for various times and at various temperatures in formaldehydesolutions. Each treatment was carried out using 45 g. of wool and 1liter of formaldehyde solution containing 4.5 g. CHzO at a pH of 4-5.The formaldehyde solutions were analyzed before and after the treatmentsto determine the amount of formaldehyde which had combined with the woolin each instance, after which the samples were thoroughly rinsed toremove uncombined formaldehyde. The samples so treated were thenbleached at 180 F. for 1 hour in peroxide solutions containing 3 g. H202and 5 g. sodium pyrophosphate per liter at a pH of 9.6. The results ofthese tests are shown in Table 2.

able 2 Table 1 Formaldehyde Percent Alkali Solubility Percent TreatmentPercent Alkali Bleaching Conditmns (percent) whiteness Test CombinedSoluble fiig Test omo after 9 ess Min. F. Bleach g. H1O: Temp. Time NoPre- Pre- No Pre- Preperl. (F.) (Hi-s.) treat. treat. treat. treat.

. l9 3 120 8 l8 10 70 67 10 150 0. 83 14 3 120 28 28 14 71 68 2 150 0.79 14 69 6 120 8 13 7 5 180 0. 97 10 69 6 1g 6 74 73 2 180 0. 79 11 69 3none 2 3 180 1 33 15 72 69 7 70 G Blank (scour only) 11 54.5 EXABH LE 3The alkali solubilities were determined by treat ing the wool sample for1 hour at 65 C. (149 F.) with 0.1 N NaOI-I solution using a 1:1000 wool:liquor weight ratio. The wool was then recovered on a Biichner funnel,washed with 2 liters of distilled water, dried to constant Weight at 105C. (221 C.) and weighed. The percent weight loss based on the dry weightof the original sample was then calculated. The alkali solubility thusrepresents the weight percent of the wool which is dissolved by 0.1 NNaOH under the conditions described.

The "percent whiteness is a measure of the degree of bleaching obtained.It is determined by a Hunter multipurpose reflectometer. The use of thismachine for measurements of this type is fully described in Bureau ofStandards Research Paper RP 1345.

It will be noted from Table 1 that the efiectiveness of the bleach atany given temperature was about the same whether or not the wool waspretreated with formaldehyde. On the other hand, the alkali solubilitiesafter bleaching were outstandingly lower for all samples which had beenpretreated with formaldehyde than for those which had not beenpretreated. Furthermore, the alkali solubilities of the bleached sampleswhich had been pretreated with formaldehyde were, with one exception,but slightly higher than the corresponding value for the blank samplewhich had been scoured only, showing that wool which has been pretreatedwith formaldehyde can be effectively bleached with alkaline peroxidewithout substantial increase in alkali solubility resulting. In test D,the alkali solubility (19%) of Scoured skeins of wool were soaked forvarying periods of time at 180 F. in a 0.9% formaldehyde solution havinga pH of 4-5, employing 225 g. of wool for each liter of solution. Theamount of combined formaldehyde was determined in each case as indicatedin Example 2. Each 45 g. skein was rinsed thoroughly to remove excessformaldehyde then bleached for 1 hour at 180 F. in 1 liter of a solutioncontaining 3 g. H202 and 5 g. sodium pyrophosphate. The alkalisolubilities of the bleached samples were then determined and are shownin Table 3 along with the values for percent combined formaldehyde.

The time required in the formaldehyde pretreatment to obtain a combinedformaldehyde value of at least 0.3% will depend on the concentration offormaldehyde in the treating solution as well as upon the temperature.Thus,

treatment of wool at F. with a 0.045% solution for 10 and 30 minutesresulted in combined formaldehyd values of 0.09 and 0.11%, respectively,whereas a value of 0.5% was obtained in 10 minutes at the sametemperature using a 0.36% solution.

Pretreatment of the wool as indicated permits the use of alkalineperoxide bleaching solutions at higher temperatures than would otherwisebe possible without excessive damage to the wool resulting. Also, morealkaline solutions may be used. Generally, the alkalinity of the bleachsolution will correspond to a pH of about 8.5 to 10.5 but is preferablyabout 9 to 10. While the pretreatment will afford worthwhile protectionagainst damage during bleaching at any temperature, e. g., up to theboiling point of the bleach bath, bleaching will generally besufiiciently rapid at temperatures of about 160- 190 R, which arepreferred, so that higher temperatures seldom will be required. At thepreferred temperatures the same degree of bleach may be obtained in buta fraction of the time required at the conventional lower temperaturesand with no greater damage to the wool. Some degradation of the wool, ofcourse, does result at such high temperatures but the amount thereof isslight providing the bleaching treatment is not prolonged beyond therelatively short period required to give the maximum bleach.

The concentration of peroxide in the bleach solution is not particularlycritical and the concentrations usually employed in prior alkalineperoxide bleaching methods, e. g., about 0.1 to 2% and preferably 0.2 to0.5%, are satisfactory. Hydrogen peroxide or any peroxygen type compoundknown to yield active oxygen under the conditions of use may be employedas the source "or active oxygen in the bleach bath. Examples of suchcompounds are the alkali metal peroxides, perborates, percarbonates andperphosphates; peracids such as peracetic acid and persulfuric acid; andthe organic peroxygen compounds such as urea peroxide, tertiary butylhydrogen peroxide and benzoyl peroxide. For economic reasons the use ofhydrogen peroxide, sodium peroxide or sodium perborate is preferred. Asis common practice in the use of alkaline bleach baths in which theactive bleaching agent is a peroxygen type compound, a peroxidestabilizer will generally be added to the bath. Many stabilizers areknown for this purpose such as the silicates, tin compounds, magnesiumcompounds and the like. The use of alkali metal pyrophosphates,particularly sodium pyrophosphate, is preferred.

I claim:

, 1. The method of bleaching wool comprising contacting the wool whichis to be bleached with a solution consisting essentially of formaldehydedissolved in water, said solution having a pH of 2xto 10 and a CHzOcontent of 0.1 to 5%; cont'nuing said contact until the combinedformaldehyde content of said wool is at least 0.3%, based on the weightof the wool; then, without intermediate chemical treatment, bleachingthe wool with an alkaline aqueous peroxide solution at a temperature ofat least F.

22; The method of bleaching wool comprising contacting the wool which isto be bleached with an aqueous solution consisting essentially offormaldehyde dissolved in water, said solution having a pH of 4 to 9 anda CH2O content of 0.3 to 2%; continuing said contact at a temperature of120 to 180 F. until the combined formaldehyde content of said wool is0.5 to 1%, based on the weight of the wool; removing from the woolformaldehyde in excess of the combined content; then, withoutintermediate chemical treatment, bleaching the wool with an aqueousperoxide solution having a pH of 8.5 to 10.5 at a temperature of about-190 F.

3. The method of claim 2 wherein the bleaching step is carried out usinga peroxide solution having a pH of 9 to 10 and containing 0.1 to 2%H202.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 787,923 Kann Apr. 25, 1905 1,713,641 Bohm May 21, 19291,978,800 Levy Oct. 30, 1934 2,077,103 Franz Apr. 13, 1937 2,220,426Pratt Nov. 5, 1940 2,220,805 Pratt Nov. 5, 1940 2,422,586 Royer June 17,1947 2,427,097 Kamlet Sept. 9, 1947 FOREIGN PATENTS Number Country Date13,088 Great Britain 1911 181,698 Great Britain Sept. 24, 1923 28,115Great Britain 1897 345,406 Great Britain Mar. 26, 1931 OTHER REFERENCESTechnicus, Textile Finishing Faults, Textile Colorist, May 1944, pp.201-203.

1. THE METHOD OF BLEACHING WOOL COMPRISING CONTACTING THE WOOL WHICH ISTO BE BLEACHED WITH A SOLUTION CONSISTING ESSENTIALLY OF FORMALDEHYDEDISSOLVED IN WATER, SAID SOLUTION HAVING A PH OF 2 TO 10 AND A CH2OCONTENT OF 0.1 TO 5%; CONTINUING SAID CONTACT UNTIL THE COMBINEDFORMALDEHYDE CONTENT OF SAID WOOL IS AT LEAST 0.3%, BASED ON THE WEIGHTOF THE WOOL; THEN, WITHOUT INTERMEDIATE CHEMICAL TREATMENT, BLEACHINGTHE WOOL WITH AN ALKALINE AQUEOUS PEROXIDE SOLUTION AT A TEMPERATURE OFAT LEAST 120* F.